Pinched poly fuse

ABSTRACT

An electrical fuse has a region of a first conductivity type in a continuous type polysilicon of a second conductivity type that is opposite the first conductivity type. In one embodiment of the invention the PN junction between the region and the poly fuse is reverse biased.

CROSS-REFERENCED TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/869,862 filed Oct. 10, 2007. That application is hereby incorporatedby reference.

FIELD OF THE INVENTION

This invention relates to electrically blown fuses in, or packaged with,semiconductor devices, and more particularly, to polysiliconelectrically blown fuses.

BACKGROUND OF THE INVENTION

Polysilicon fuses are used in semiconductor devices or packages due totheir advantages including the ability to be blown without an opening toallow fused by-products to escape as required with metal fuses.Polysilicon fuses can thus be used for trimming during wafer sort, finaltest, and in customer applications.

Typically polysilicon fuses have a layer of silicide over the fuse toform a low resistance conductor for the current densities required togenerate the heat to create a discontinuity in the polysilicon and inthe silicide. However, the fuse must be designed, and the proper fusecurrent must be used to prevent the silicide flows from reforming theelectrical connection across the fuse after it has been initially blown.

SUMMARY OF THE INVENTION

The invention comprises, in one form thereof, an electrical fuse havinga region of a first conductivity type in a continuous polysilicon fuseof a second conductivity type opposite the first conductivity type.

In another form, the invention includes a method of forming apolysilicon fuse. The method comprises the steps of forming a firstregion of a continuous type polysilicon and forming a second region of aconductivity type opposite to the first region.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned and other features, characteristics, advantages, andthe invention in general will be better understood from the followingmore detailed description taken in conjunction with the accompanyingdrawings, in which:

FIGS. 1A and 1B are respective top and side views of a first embodimentof a pinched poly fuse according to the present invention;

FIGS. 2A and 2B are respective top and side views of a second embodimentof a pinched poly fuse according to the present invention;

FIGS. 3A and 3B are respective top and side views of a third embodimentof a pinched poly fuse according to the present invention;

FIGS. 4A and 4B are respective top and side views of a fourth embodimentof a pinched poly fuse according to the present invention;

FIGS. 5A and 5B are respective top and side views of a fifth embodimentof a pinched poly fuse according to the present invention;

FIG. 5C is a side view of the pinched poly fuse shown in FIG. 5A with areverse bias voltage applied to the PN junction;

FIGS. 6A and 6B are respective top and side views of a sixth embodimentof a pinched poly fuse according to the present invention; and

FIG. 6C is a side view of the pinched poly fuse shown in FIG. 6A with areverse bias voltage applied to the PN junction.

It will be appreciated that for purposes of clarity and where deemedappropriate, reference numerals have been repeated in the figures toindicate corresponding features. Also, the relative size of variousobjects in the drawings has in some cases been distorted to more clearlyshow the invention.

DETAILED DESCRIPTION

Turning now to the drawings, FIGS. 1A and 1B are respective top and sideviews of a first embodiment of a pinched poly fuse 10 according to thepresent invention. The poly fuse 10 has a “bow tie” configuration with apositive terminal 12 and a negative terminal 14 having respectivesilicide layers 16 and 18, which are formed using platinum in oneembodiment of the present invention, over a portion of N+ polysilicon20. The terminals 12 and 14 have respective neck-down regions 24 and 26where the silicide layers 16, 18 end leaving only the polysilicon 20.Between the neck-down regions 24, 26 is a relatively narrow strip of acontinuous type of polysilicon 28. In FIG. 1 the continuous type is N+.The polysilicon 20 is N+ except for an elongated P+ region 30 formed inthe polysilicon 28 which extends from the top surface of the polysilicon28 downward but not extending all the way to the bottom surface of thepolysilicon 28.

The P+ region 30, formed by counter doping the N+ polysilicon 20,effectively “pinches” the N+ polysilicon 20 to concentrate the electronand hole carriers into a narrower region. Simulation has shown that thehottest portion of the N+ polysilicon 20 is where the electrons exitfrom the high concentration region under the P+ region 30 as indicatedby the reference letter “T” in FIG. 1A. T is the trim line where the N+polysilicon 20 starts to open. As the N+ polysilicon 20 heats up andstarts to lose its conductivity, the N+ polysilicon 20 is further“pinched” thus causing a rapid breakdown in the polysilicon at the trimline T.

In FIGS. 1A and 1B the suicide layers 16, 18 do not extend near enoughto the trim line T to where the N+ polysilicon 20 heating will result inthe platinum (in the case of a platinum silicide) melting and flowingacross the fuse element.

FIGS. 2A and 2B are respective top and side views of a second embodimentof a pinched poly fuse 34 according to the present invention in whichthe silicide 36 at the negative terminal extends over and contacts theP+ region 30 to reverse bias the junction between the N+ polysilicon 20and the P+ region 30. It is believed that with a reverse bias thedepletion region in the N+ polysilicon 20 around the P+ region 30 willfurther “pinch” the conductive region in the N+ polysilicon 20 under theP+ region 30.

FIGS. 3A and 3B are respective top and side views of a third embodimentof a pinched poly fuse 38 according to the present invention whichreverse dopant types as those in FIGS. 1A and 1B. Thus the pinched polyfuse 38 shown in FIGS. 3A and 3B have P+ polysilicon 40 extending fromunder the silicide 16 at the positive terminal of the pinched poly fuse38 to under the silicide 18 at the negative terminal of the pinched polyfuse 38, respectively. Between the neck-down regions 24, 26 is therelatively narrow strip of continuous type polysilicon 28 with an N+region 50 formed in the polysilicon strip 28. In FIG. 3 the continuoustype is P+. It is believed that the pinched poly fuse 38 will have thesame characteristics as the pinched poly fuse 10 of FIGS. 1A and 1B.

FIGS. 4A and 4B are respective top and side views of a fourth embodimentof a pinched poly fuse 54 according to the present invention and differsfrom the embodiment shown in FIGS. 3A and 3B in that the silicide layer56 at the positive terminal 12 extends over and contacts the N+ region50 to reverse bias the PN junction between the P+ polysilicon 40 and theN+ region 50. Although the silicide layer 56 extends across the trimorigin T, it does not form a conductive path across the trim origin Tand therefore does not interfere with the pinching of the P+ polysilicon40 by the N+ region 50. Thus the silicide layer 56 does not necessarilyhave to be separated at the trim origin T when the pinched poly fuse 54is opened as long as there is not a conductive path from the positiveterminal 12 and the negative terminal 14 through the P+ polysilicon 40.In this situation the silicide layer 56 would be at the positive voltageat the positive terminal but would only be in contact with the P+polysilicon 40 on the positive portion of the interrupted polysiliconand with the N+ region 50 which forms a reverse biased PN junction withthe negative portion of the P+ region 50 connected to the negativeterminal 14.

FIGS. 5A and 5B are respective top and side views of a fifth embodimentof a pinched poly fuse 60 according to the present invention and differsfrom the previous embodiments in that there is no silicide. In otherwords FIGS. 5A and 5B are FIGS. 1A and 1B, respectively, without anysilicide.

FIG. 5C is a side view of the pinched poly fuse 60 shown in FIG. 5A witha reverse bias voltage 62 applied to the PN junction formed by the N+polysilicon 28 and the P+ region 30. The reverse bias voltage would havethe same effect as the reverse bias applied to the pinched poly fuse 34shown in FIG. 2B is the voltage potential of the reverse bias voltage isthe same as the voltage potential as the voltage difference between thepositive terminal 12 and the negative terminal 14 of FIG. 2B. However,in FIG. 5C the magnitude of the reverse bias potential could be higheror lower than the magnitude of the reverse bias potential of FIG. 2Boffering the possibility of optimizing the reverse bias voltage acrossthe PN junction of FIG. 5C.

FIGS. 6A, 6B, and 6C are respective top and two side views of a fifthembodiment of a pinched poly fuse 70 according to the present invention.The pinched poly fuse 70 has doped polysilicon that is the complement ofthe doped polysilicon of FIGS. 5A, 5B, and 5C in the same manner as thedoped polysilicon of FIG. 2A is the complement of the doped polysiliconof FIG. 1A. It is believed that the operating characteristics of thepinched poly fuse 70 will be the same as the those of the pinched polyfuse 60.

While the invention has been described with reference to particularembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from thescope of the invention.

Therefore, it is intended that the invention not be limited to theparticular embodiments disclosed as the best mode contemplated forcarrying out this invention, but that the invention will include allembodiments falling within the scope and spirit of the appended claims.

1. An electrical fuse comprising: a body of continuous polysiliconhaving first and second terminals ends and an elongated central portiondisposed between the terminal ends wherein the terminal ends are widerthan the elongated central portion; the body of continuous polysilicondoped with a dopant of first polarity; and a region of the elongatedcentral portion of the body doped with a dopant of second polarityopposite to the first polarity.
 2. The fuse of claim 1 wherein thelength of the elongated central portion is longer than the length ofeach terminal end.
 3. The fuse of claim 1 wherein the body of continuouspolysilicon is heavily doped with dopants of first polarity.
 4. The fuseof claim 3 wherein the region of the elongated central portion isheavily doped with dopants of second polarity.
 5. The fuse of claim 3wherein the body of continuous polysilicon is N+ doped and the region ofthe elongated central portion is P+ doped.
 6. The fuse of claim 3wherein the body of continuous polysilicon is P+ doped and the region ofthe elongated central portion is N+ doped.
 7. A method for forming anelectrical fuse comprising: providing a substrate; forming a body ofcontinuous polysilicon on said substrate, said body having first andsecond terminals ends and an elongated central portion disposed betweenthe terminal ends wherein the terminal ends are wider than the elongatedcentral portion; doping the body of continuous polysilicon with a dopantof first polarity; and doping a region of the elongated central portionof the body with a dopant of second polarity opposite to the firstpolarity.
 8. The method of claim 7 wherein the length of the elongatedcentral portion is longer than the length of each terminal end.
 9. Themethod of claim 7 wherein the body of continuous polysilicon is heavilydoped with dopants of first polarity.
 10. The method of claim 7 whereinthe region of the elongated central portion is heavily doped withdopants of second polarity.
 11. The method of claim 10 wherein the bodyof continuous polysilicon is N+ doped and the region of the elongatedcentral portion is P+ doped.
 12. The method of claim 10 wherein the bodyof continuous polysilicon is P+ doped and the region of the elongatedcentral portion is N+ doped.